Whole-body biodistribution of [18F]SMBT-1: a novel PET tracer for monoamine oxidase B imaging in healthy humans

OBJECTIVE: [18F]SMBT-1 is a selective and reversible monoamine oxidase B (MAO-B) radiotracer used for astrogliosis imaging. This study aimed to observe the whole-body biodistribution of [¹⁸F]SMBT-1 and evaluate peripheral MAO-B expression in healthy human volunteers using dynamic positron emission tomography (PET) imaging. METHODS: Six healthy subjects (four males, two females; age range: 21–63 years) underwent nine dynamic PET scans over 5.5 h after [18F]SMBT-1 injection. The first five emission scans were acquired consecutively in a single session within 30 min (min) of post-injection (p.i.). The remaining four emission scans were performed at 70–110, 150–180, 220–250, and 290–330 min p.i. Regions of interest (ROIs) were manually drawn on the co-registered PET and magnetic resonance imaging (MRI) for the selected organs to extract mean standardized uptake values (SUVmean) and generate time-activity curves (TACs). RESULTS: A significantly high early uptake of [18F]SMBT-1 was observed in the kidneys, liver, heart, and stomach between 5 and 30 min p.i. The kidneys showed the highest early peak at 5 min p.i. (SUVmean = 14.2 ± 3.5). The gallbladder and intestines exhibited a delayed uptake pattern, with the gallbladder SUVmean increasing substantially from 9.0 ± 4.2 at 30 min to 123.7 ± 53.4 at 330 min. No significant differences in tracer uptake patterns were observed across participants. CONCLUSION: [¹⁸F]SMBT-1 exhibited favorable reversible kinetics in the whole-body biodistribution assessment, confirming its established utility for imaging reactive astrocytes and indicating its potential for future applications in systemic high MAO-B-related pathologies.